VFW 614 / ATTAS

28 May 2010

Flying quick-change artist

The DLR VFW 614/ATTAS research aircraft

For more than twenty years, ATTAS (Advanced Technologies Testing Aircraft System) has been the large flying test bed of the German Aerospace Center (DLR). ATTAS was primarily designed as a 'flying simulator', to simulate the flying behaviour of other - real (existing) or virtual - aircraft.

The application portfolio of ATTAS is very wide-ranging. With its measurement and test equipment, ATTAS is used for numerous test duties, such as testing future air traffic control procedures and low-noise approaches, for example. Research into wake vortices is also carried out with ATTAS; these are air turbulences that occur as a result of the lift produced on the wings.

ATTAS is based on the 44-seater, twin-engine VFW 614 short-haul jet developed in the 1970s by Bremen-based VFW Fokker (now Airbus).

One of the core modifications was the integration of an electrohydraulic fly-by-wire flight control system (FBW), in addition to the usual mechanical controls. The changeover from mechanical to electronic control can be made as required during the test flight. This enables scientists and engineers to investigate anything and everything that is possible with a computer in terms of flight control.

ATTAS was converted to a research aircraft at the end of the 1980s and since then has been used for aviation research for an average of 130 flying hours per year. Today, however, ATTAS is the last example in the world of the VFW 614 still flying. As a result, the supply of spares is limited to those currently held in stock, and the aircraft is inevitably approaching the end of its operating life. The youngest member of the fleet, the Airbus A320 ATRA (Advanced Technology Research Aircraft) will succeed ATTAS from the end of 2008.

Modifications

The following modifications differentiate ATTAS from the standard VFW 614:

General view of the electrohydraulic, fly-by-wire flight control system

Electrohydraulic, digital fly-by-wire flight control system. It intervenes in the standard mechanical-hydraulic steering via electrohydraulically-operated linkages, which are connected to the control units of the safety pilot sitting on the right. The safety pilot can disconnect the fly-by-wire linkages at any time and take over control with the mechanical system. The fly-by-wire flight control system covers aileron, elevator, rudder, trimmable stabiliser, engines, landing flaps and the direct lift control flaps in the rear section of the landing flaps. The fast-moving flaps enable a direct change to the wing lift and so provide an additional degree of freedom in the longitudinal motion of the aircraft, which, amongst other things, is necessary for the in-flight simulation used in assessing the flight characteristics.

Computer system for controlling the electronic fly-by-wire flight control system, with freely programmable, powerful experimental computer. The installed simulation software can simulate the flight behaviour of other (even virtual) aircraft. Because of the safety concept with the mechanical back-up control system, the software used does not need to be certified. The experimental system can be expanded with additional computer modules.

Test pilot cockpit with freely programmable displays, fitted with both a sidestick and a control column.

Measurement system for recording and displaying the data from the flow and acceleration sensors, avionics and air data, data from the FBW flight control system, and additional data from the computer system.

Electrical and hydraulic power supplies for the experimental systems, independent of the systems of the basic aircraft.

Missions - research focus

Research into the life and decay of wake vortices

The aim of the experiments is to reduce the possible separation distance between aircraft coming in to land or taking off behind one another, by means of a more accurate computation of the evolution and decay of wake vortices. For this, the wake vortex produced by ATTAS is measured by LIDAR (Light Detection and Ranging) systems either stationed on the ground or installed in an aircraft. At the same time, there was also the attempt to accelerate the breakdown of the wake vortex by periodic aileron movements.

Simulation of flying through wake vortices

Visualisation of a wake vortex

Using a simulation programme, and with the help of the fly-by-wire flight control system, flying into wake vortices is simulated without risk; and then, based on the pilot's subsequent assessment, criteria are developed for possible, acceptable vorticities. Strategies for automatic countersteering will be tested too.

Testing future air traffic control procedures

Thanks to satellite navigation, aircraft today are able to navigate very precisely, independently of ground-based support systems. Over and above this, to enable optimal planning and control of air traffic, individual airspace users need to be managed with the timings as accurate as possible in that airspace. The solution lies in trajectories - so-called 4D trajectories - which describe the route of an aircraft precisely in both the time and space domains, and enable each individual leg of the flight to be strategically planned. This way, conflicts in the airspace can be detected and avoided more effectively. Finally, this capability will lead to higher airspace and airport capacities.

The DLR Institute of Flight Guidance (DLR-Institut für Flugführung) has already developed and tested an Advanced Flight Management System (AFMS) back in the 1990s, a system that makes precisely this 4D planning and management possible. Since then the system has been continuously improved. Additions include communication elements that link the traffic planning modules on the ground to the flight route planning modules in the aircraft by data link.

The AFMS has already demonstrated its highly promising capabilities in numerous test flights with ATTAS, the DLR research aircraft.

Testing new low-noise approach procedures

With the Experimental Flight Management System, the approach profile is worked out accurately - depending on the wind and other factors - whilst the aircraft is still at cruising altitude, and then flown along fully automatically and with accurate timing. This enables, for example, low-noise steep approaches with the engines idling, and approaches to the ILS glide path from above that would not be possible with a conventional flight management system.

Technical data

ATTAS

Length:

20.60 metres (24.39 metres with nose boom)

Height:

7.84 metres

Wingspan:

21.50 metres

Wing area:

64 square metres

Cabin width:

2.66 metres

Cabin height:

1.92 metres

Seats:

For DLR research: three seats for crew members and up to seven seats for scientists. The basic model VFW 614 had up to 44 seats.